1. Field of the Disclosure
This disclosure relates to a liquid crystal display device, and more particularly to a liquid crystal display device with an improved contrast ratio and a reduced electric power consumption, and a driving method thereof.
2. Description of the Related Art
As the information society grows, flat display devices capable of displaying information have been widely developed. These flat display devices include liquid crystal display (LCD) devices, organic electro-luminescence display (OLED) devices, plasma display devices, and field emission display devices. Among the above display devices, LCD devices have the advantages that they are light, small, provide a low power drive and have a full color scheme. Accordingly, LCD devices have been widely used for mobile phones, navigation systems, portable computers, televisions and so on. An LCD device controls the transmittance of a liquid crystal on a liquid crystal panel, thereby displaying a desired image.
FIG. 1 is a block diagram schematically showing an LCD device of the related art. Referring to FIG. 1, the LCD device includes a timing controller 1, a gate driver 2, a data driver 3, a liquid crystal panel 4, a backlight controller 5, a backlight driver 6, and a backlight unit 7.
The timing controller 1 receives control signals including a vertical synchronous signal, a horizontal synchronous signal, a data enable signal, a data clock and others, together with a data signal from the exterior. From the vertical and horizontal synchronous signals, the data clock, and the data enable signal, the timing controller 1 generates first control signals for driving the gate driver 2 and second control signals for driving the data driver 3. Moreover, the timing controller 1 generates a backlight control signal for controlling the backlight controller 5.
The first control signals enable the gate driver 2 to apply scan signals to the liquid crystal panel 4. The second control signals enable the data driver 3 to convert the data signal into an analog data voltage and to apply the converted analog data voltage to the liquid crystal panel 4.
The backlight controller 5 generates a backlight drive signal in accordance with the backlight control signal and applies the backlight drive signal to the backlight driver 6. The backlight driver 6 supplies the backlight unit 7 with a drive voltage derived from the backlight drive signal. The backlight unit 7 irradiates a light corresponding to the drive voltage onto the liquid crystal panel 4.
The liquid crystal panel 4 displays an image according to the refractive index of the liquid crystal which is interposed between two substrates. More specifically, the refractive index of the liquid crystal is varied along with the drive voltage and a transmissive amount of light, which is transmitted through from the backlight unit 7, is adjusted in accordance with the refractive index of the liquid crystal, thereby displaying the image.
In general, the LCD device has been forcibly required to have a high contrast ratio which allows dark and bright regions in an image to be more darkly and brightly displayed, respectively. This results from the fact that the LCD device must have a higher contrast ratio in order to reproduce a more defined image.
However, since the related art backlight unit 7 is driven by a fixed backlight control signal, it is impossible to realize the high contrast ratio in the LCD device. This backlight driving system has been referred to as a “normal brightness control system”.
Recently, a global brightness control system has been proposed which analyzes the image of a single frame and then controls the brightness and modulates the image according to the analyzed resultant. The global brightness control system can control the brightness for an image of a single frame, but cannot control brightness for a local image (i.e., a portion of the image). In other words, a local high contrast ratio cannot be obtained by the global brightness control system.
To address this matter, a local brightness control system has been proposed which divides a single frame image into a plurality of local images and controls the brightness corresponding to each of the divided local images. However, the local brightness control system has lower brightness than that of the normal brightness control system, in a middle/high gray level range of about 60˜200.
In addition, all of the normal, global, and local brightness control systems force electric power consumption to be increased.